The world needs to triple the energy it gets from renewables, nuclear reactors and power plants that use emissions-capture technology to avoid dangerous levels of global warming, United Nations scientists said.

Investments needed to keep climate change within safe limits would shave a fraction of a percent off annual global growth, the UN said today in the third part of its most comprehensive study on warming. A delay in stemming rising greenhouse gases will cut chances to limit the global temperature increase, add to costs and lead to increasingly reliance on unproven technologies, they said.

“The longer we wait to implement climate policy, the more risky the options we’ll have to take,” Ottmar Edenhofer, a co-chair of the 235 scientists who drafted the report, said in a phone interview from Berlin. “We need to depart from business as usual, and this departure is a huge technological and institutional challenge.”

The UN said governments must accelerate efforts to build wind farms and solar parks and provide incentives to develop carbon capture and storage technology, or CCS, for fossil-fuel plants by making it more costly to emit carbon. The study aims to guide envoys from 194 nations next year as they devise a new accord to slash greenhouse gases.

The researchers said emissions growth accelerated to an average of 2.2 percent a year for the 2000-2010 period from an annual 1.3 percent the preceding three decades. That puts in jeopardy the target agreed upon by climate treaty negotiators to stabilize warming since pre-industrial times to below 2 degrees Celsius (3.6 degrees Fahrenheit).

‘Too Long’

The possible situation in 2100 is “either you’ll have some fossil-fuel power generation with carbon capture and storage, or a complete switchover to renewables and smart energy storage,” Jonathan Grant, director of climate change at consultants PwC in London, said by phone. “The problem with some of those scenarios is the transition takes too long.”

Global greenhouse gas emissions would have to be lowered between 40 percent and 70 percent by mid-century from 2010 levels, and to “near-zero” by the end of the century, efforts that would be likely to limit warming to 2 degrees Celsius, the UN Intergovernmental Panel on Climate Change said today in a statement handed out in Berlin.

Without extra effort to cut greenhouse gases, current trends may triple their concentration in the atmosphere this century, pushing warming since 1750 from 3.7 degrees Celsius to 4.8 degrees Celsius, according to the report. That would raise the risk of melting glaciers and sea ice, lengthening droughts and heatwaves and intensifying storms and flooding.

‘Unprecedented’ Cooperation

“This report brings out the need for an unprecedented level of international cooperation,” Rajendra Pachauri, chairman of the IPCC, told reporters today in Berlin.

The assessment by the IPCC is intended as a reference for officials around the world as they devise emissions-curbing policies. Hundreds of scientists and government officials have spent the past week in Berlin editing a draft line-by-line to put it into clearer wording understandable to policy makers.

When the panel finished its last study seven years ago, it was rewarded with the Nobel Peace Prize and the prospect its findings might spur a globally binding treaty to cut greenhouse gases. That deal hasn’t yet materialized, and the scientists were criticized for inaccuracies in their work and the content of leaked e-mails between climate researchers.

Health Benefits

The new report says measures to cut emissions may cost as much as 4 percent of global consumption in 2030 and 11 percent in 2100, in line with figures included in a draft report that was leaked in January. The figures don’t include benefits of the expenditure, such as better health due to improved air quality.

Countries including the U.S. and the U.K. said the cost numbers risked skewing the data and lending support to those skeptical of spending money to tackle climate change. To allay those concerns, the researchers added language to show the costs are the cumulative effect of shaving about 0.06 percentage points off annual consumption growth that’s projected to be 1.6 percent to 3 percent.

“This report is a wake-up call about global economic opportunity we can seize today as we lead on climate change,” U.S. Secretary of State John Kerry said in an e-mailed statement.

Power Investment

The International Energy Agency estimated last year that the power industry needs to invest $17 trillion from 2013 through 2035 to satisfy rising electricity demand. Investments made now in new fossil fuel-fired plants have implications for future emissions because they last for decades, it says.

“After the boom of coal in the last decade, the 21st century is now the century of renewable energies,” Martin Kaiser, climate policy analyst at the environmental group Greenpeace, said in an interview. “That means a transition period of 20 to 30 years. That has to be organized and has to come quickly.”

To meet the 2-degree goal, annual spending on fossil fuel plants must drop by $30 billion a year by 2030, the panel said. Annual expenditure on renewables, nuclear, and carbon capture and storage must rise by $147 billion, and spending on energy efficiency measures for transportation, buildings and industry needs to increase by $336 billion, it said.

Industry Boon

“Substantial reductions in emissions would require large changes in investment patterns,” the scientists wrote. A 2-degree scenario would involve “more rapid improvements of energy efficiency, a tripling to nearly a quadrupling of the share of zero- and low-carbon energy supply” by 2050.

Existing emissions pledges by nations that are working toward a new international deal on climate change aren’t enough to meet the temperature target in the most cost-effective way, the scientists said. The longer we delay in reducing emissions, the more reliant we’ll be on carbon capture, a relatively unproven technology, they said.

CCS has been installed on an industrial scale in 12 facilities worldwide, none of them in power stations, according to the Global CCS Institute in Melbourne, Australia.

Injecting CO2

Operational plants include Statoil ASA (STL)’s Sleipner project, in which carbon dioxide, or CO2, is siphoned out of natural gas and injected into saline aquifers, and a program at a Koch Nitrogen Co. fertilizer plant in Oklahoma that pipes CO2 to oil fields for enhanced oil recovery. Southern Co.’s Kemper project in Mississippi and a SaskPower International Inc. project in Saskatchewan, Canada, are set this year to become the first two power stations equipped with CCS.

Governments need to bring in policies that boost the cost of emitting carbon to a level that make CCS “economic,” Michael Grubb, chair of the Cambridge Centre for Climate Change Mitigation Research at the University of Cambridge, said in a phone interview. He put the level at more than 50 euros ($69) per ton. Allowances currently trade at about 5 euros on the European Union emissions trading system, the world’s biggest.

Edenhofer, chief economist at the Potsdam Institute for Climate Impact Research in Germany, said CCS will be “indispensable,” as will its combination with bioenergy, which in theory will lead to negative emissions. That’s because the plants grown to fuel a biomass-fired power plant suck CO2 out of the atmosphere, while the CCS equipment would pipe the plant’s emissions for permanent underground storage.

Behavioral Changes

Other emissions-cutting tools identified by the panel include energy-saving measures for buildings such as insulation, more efficient machinery for factories and stricter fuel standards for vehicles. Behavioral changes were also deemed a “key mitigation strategy.” Those could include changing modes of transportation, altering diets and cutting food waste, they said.

“The cost of averting catastrophic climate change is minimal, but in order to keep costs down, we have to act now,” said Samantha Smith, who leads the climate program at the environmental group WWF. “It is going to take coordinated efforts and it can’t be done by individual countries, companies or individuals each doing their very best.”